Numerous types of roof assemblies have previously been proposed for pre-engineered buildings in efforts to provide a watertight roof assembly, while also enabling the roof assembly to expand and contract as changes in temperature are encountered. Typical of such prior art roof assemblies of considerable success in recent years is the  standing seam roof assembly.
The panel members of the standing seam roof assembly are joined along lapped together side edges forming the standing seams. The panel members are secured to secondary structural members by either clips or through fasteners. The clips used to attach to the standing seam can be of two types: floating (one or two piece moveable); or fixed (one piece with no movement allowed between the panel and the supporting structure). Through fasteners penetrate the panels and attach the panels to underlying support structure to substantially lock the panels and support structure together so that differential movement is restricted. Roofs may be classified as shed roofs and low slope gasket roofs. Shed roofs are roofs that shed water because gravity pulls the water down and away from panel joints more effectively than wind or capillary action propel water thought the joint. Shed roofs generally occur over slopes of three to twelve or greater. Low slope gasket roofs, on the other hand, provide roof joints that are made watertight by placing gasket material between the panel joints and securing the gasket material in place by, for example, encapsulating or exerting pressure on the gasket material. Generally, low slope gasket roofs have a one to twelve or less slope.
Heretofore, field seamed gasket joints used on large roofs have generally been limited to using two-piece clips wherein movement between the roof and its underlying structure occurred within the clip. The reason for this is that, in the past, the line of sealant serving as the gasket and the top hook portion of the clip intersected, and if the clip hook moved in relation to the panel which held the sealant, the relative movement deformed and destroyed the gasket seal. One piece clips have been used freely in small  and shed roofs where gasket sealing was not required.
Standing seam metal roof panels exhibit considerable diaphragm strength and it is desirable to use this strength by interconnecting the panels side to side so adjacent panels do not slide relative to each other and to connect the roof to the support frame to help stabilize the support frame, rather than to brace and stabilize the support frame by other means. Past practices have been to stabilize the support frame by means of separate bracing, and on gasket roofs, to use a suitable two-piece floating(moveable) clip to allow the brace and frame to remain fixed and for the panel to move in relation to the frame when subjected to temperature changes or other forces. Alternatively, the length of the panel run was limited to no more than about 40 feet so that the expansion and contraction of the panel does not damage the connection to the underlying support structure.
The desirable result of eliminating detrimental differential movement between the panel and support structure on large roofs can also be achieved by construction of the underlying support to move slightly to accommodate the expansion and contraction of the roof due to temperature changes or other forces. One such means of construction is exemplified by the Flex Frame™ support system produced by ReRoof America, Inc., Tulsa, Okla.
The interconnected panel members of the standing seam roof lend stiffness and strength to a flexible roof structure while allowing the roof structure to expand and contract as a function of the coefficient of expansion of the panel material and the temperature cycles of the roof panels.
If floating clips or flexible framing are not used, the repeated action of expansion  and contraction of the panel member tends to weaken the panel-to-panel lap joints and the panel to framing connection, causing separation, structural failure and roof leakage. Leaks are generally caused by the weakening of the fastening members and working or kneading of the sealant disposed at the joints. Thus, prior art sealants for such roof assemblies have required the qualities of adhesion, flexibility and water repellence. Further, in many instances the pressure on the sealant can vary greatly throughout the length of the sidelap and end lap joints of the panels, resulting in uneven distribution and voids in the joint sealant.
Many of the problems encountered with prior art standing seam roofs, such as structural failures and leaks, are overcome by the standing seam floating roof assembly taught by U.S. Pat. No. 5,737,894 issued to Harold G. Simpson. The standing seam floating roof assembly is formed of elongated metal panels, each of which is provided with a female member formed along one longitudinal edge and a male member formed along the opposed longitudinal edge. Adjacently disposed panels are joined by interlocking female and male members to form the standing seam joint. Clips interconnect the standing seam joints and the supporting structure, with the upper portions of the clips hooking over the male members of the panels. Most such clips are of the sliding type which permit the hooking portions to move relative to supporting base portions connected to the supporting structure, while relative motion between the clip hooks and the metal panels is substantially prevented. A sealant material is disposed to form a moisture dam in the interlocking joints of the female and male members. 
In addition to the use of standing seam roof assemblies on newly constructed pre-engineered buildings, standing seam roof assemblies are also finding increased usage in another segment of the roofing industry, that of built up roof replacement. Generally, a built-up roof is formed of a plurality of sections which are interconnected and over coated with asphaltic composition to provide a watertight seal. While such roofs have generally served successfully, problems have been encountered as built-up roofs age, when the buildings settle and when construction errors have resulted in standing water pockets. Standing water usually results in deterioration of the roof, resulting in leaks and other problems.
A need has long been recognized for replacing a roof without making substantial modifications to the existing roof. In addition to being economical fabrication and on-site construction, it is highly desirable that the new roof assembly be capable of providing a new roof surface independent of the variations in the surface of the preexisting roof. Past repair methods, especially those capable of altering the roof slope to improve drainage, are excessively time consuming and require substantial destruction of the original roof and extensive custom construction, thus exposing the building and its contents to damage by the elements during the reroofing process.